Two days after a young off-duty officer was fatally shot at a taco stand in Lincoln Heights, police were still looking for the gunman who killed him.

Juan Jose Diaz, 24, was eating near the stand shortly after midnight Saturday with his girlfriend and her two brothers when he saw someone tagging a wall, according to law enforcement sources. Diaz told the person to stop, spurring a confrontation that led to his death.

Diaz was pronounced dead at the scene close to Avenue 26 and Humboldt Street. His girlfriend’s brother was taken to a hospital for treatment.

Outside Diaz’s family home in Cypress Park on Sunday, a longtime friend of the officer told the Los Angeles Times that Diaz wanted to make a difference in his city.

Gang activity plagued Cypress Park when they were growing up there in the early 2000s, said Eduardo, who declined to give his last name because the suspect may be a gang member. Drive-by shootings were common in the neighborhood just three miles north of Lincoln Heights. As teenagers, they were stopped and questioned by LAPD officers while riding bikes in the area.

The encounters were scary, Eduardo said, and they felt that the police treated them unfairly. He thinks that may have motivated Diaz to pursue a job in law enforcement.

“He wanted to be that cop that was not categorized as a bad cop,” Eduardo said. “He wanted to be the good cop.”

According to law enforcement sources, a group of young men approached Diaz sometime after the tagging exchange and began threatening him and his friends. One of the young men lifted his shirt to reveal a handgun.

The gunman claimed allegiance to the Avenues, a once-powerful gang that has lost its grip on Lincoln Heights in the last decade, the source said. The gunman told Diaz and his friends that they were in the gang’s territory. The group rushed to their car to drive away, but the gunman opened fire as they got into the vehicle.

Diaz joined the force two years ago and was assigned to the Special Operations Division, which conducts investigations into department personnel. He wanted to be a cop since preschool, a family member told mourners at a vigil for the slain officer on Saturday night.

His sister, Anahi Diaz, told the crowd their mother and father are devastated by the killing.

“I just want to remind everyone that these people are putting their lives out there for us,” she said. “We have to protect them as well; that’s the least we can do. They’re more than a badge. They’re human beings.”

Childhood friend Martin Gomez said Diaz “was never the jock, never the smart kid. He was the best kid. You could count on him for everything.”

Many at the vigil wore Dodgers clothing because Diaz loved the team.

Sgt. Manuel Hernandez, Diaz’s Police Academy sergeant, choked back tears as he remembered the cadet.

“I had no doubt that he was going to be a great police officer,” Hernandez said. “I even joked with him that I was sure I was going to be working for him one day.”